Multi-voltage input-output (I/O) integrated circuit (IC) designs are common for battery powered mobile devices. To maintain compatibility between the IC and other circuits in a system operating at different voltage levels, interface cells are used within the IC that serve as level shifters to protect lower internal voltage circuitry from higher voltages. The input-output stages of the IC can operate at different voltage levels to make output signals from the IC compatible with other components operating at differing voltage levels.
In battery powered applications, conservation of power prolongs the usefulness of the device for each battery charge. With increasing data bus widths and with systems including additional voltage domains or sections that can be powered down, increasing numbers of level shifters are required. With the increasing number of interface cells, all characteristics of the interface cell become important: layout size; quiescent power; speed; and signal symmetry.